This invention relates generally to the production of phosphor screens for color picture tubes and particularly to a system and method for intermittently moving a faceplate panel during exposure of a phosphor screen on a lighthouse.
A color picture tube includes a screen composed of triads of different phosphors which emit different colored light when excited by electrons. Typically, the screen is composed of alternating stripes of phosphors which respectively emit red, green and blue light. Positioned between the screen and the electron gun from which the exciting electrons emanate is a color selection electrode, commonly called a shadow mask. The shadow mask assures that the electron beams excite phosphor stripes of the proper color.
During the production of the phosphor screen, the entire inside surface of the panel is coated with one of the phosphors mixed in a photosensitive material. The shadow mask is then inserted into the panel and the assembly is placed onto a lighthouse which contains a light source. Light from the light source passes through the apertures in the shadow mask and exposes some of the phosphor. The panel is moved with respect to the lighthouse during the exposure. The motion causes the phosphor to be exposed in solid stripes having a width substantially equal to the width of the apertures. However, the shadow masks are made of a thin sheet of light weight metal and therefore can vibrate because of the motion. Such vibration causes the width of the stripes to vary, resulting in an objectionable affect commonly called "snake".
The instant invention is directed to a motor control system for intermittently moving kinescope panels on a lighthouse during exposure of the phosphor screen to eliminate vibration of the shadow masks, and thereby eliminate the "snake" affect caused by such vibration.